The present invention relates to a method of producing a refractory lining in a metallurgical vessel designed to contain molten metal, such as a ladle used for casting steel.
Metallurgical vessels designed to contain molten metal generally comprise a metal shell whose inner surface is covered by a lining of refractory material to avoid any direct contact between the molten metal and the shell. So far as the peripheral internal surface is concerned, the refractory metal covering it generally comprises a layer of tamped sand applied from the bottom upwards. When that sand becomes worn and its thickness becomes insufficient to ensure effective protection, one proceeds to remake the lining by covering the bottom with refractory sand slung onto it by means of a sand-slinger.
The refractory lining forming the bottom of such vessels generally consists of brickwork. This kind of construction is not entirely satisfactory, since discontinuities between bricks form weak areas through which molten metal infiltrates, thereby prematurely putting the refractory lining out of use. This disadvantage impairs the useful life of the refractory. In order to remedy this disadvantage, the applicant has already suggested the following method. One locates on the bottom of a metal shell a first removable annular mould identical in shape to the peripheral contour of the bottom so as to define, between the lateral wall of the vessel and the mould, a continuous zone equal in height to the thickness of the bottom to be built and having a sufficiently reduced width to obtain a desired homogeneous degree of compaction throughout the surface of this zone. One fills that zone with crude sand of suitable composition, the zone is tamped, and the first mould is removed. A second mould similar to the first one, but smaller in size, is then placed in position so as to define a second tamping zone, and so on, until the central zone delimited by the last mould has a width approximately equal to that of the other tamped zones.
By means of ordinary sand and without using a binder, the applicant has been able to produce bottoms whose life is longer than that of the walls, which at present is 33 castings on average. The suggested solution has been found to be very satisfactory.
The present way of producing a lining still has, however, the following drawbacks. Sintering of the refractory takes place only in the absence of humidity. On the other hand, drying of the refractory starts from the surface thereof. This results in the surface part which has been sintered first preventing to a considerable extent evaporation of water contained in the underlying sand from taking place and stopping sintering from continuing in the sand. It would thus be advantageous to systematically and uniformly dry the refractory. Such a drying operation could remedy to a great extent difficulties in the toughness of the refractory, particularly of the bottom, especially when dealing with large dimensions. Moreover, an improvement in sintering would surely result in an increase of the life of the refractory.
It should be noted, however, that a certain improvement has already been achieved by the applicant by means of the method of producing bottom linings by using the moulds referred to above. It has been suggested in that method to spread a layer of loose sand on the layer to be dried, the sand serving to prevent direct contact between a drying flame and the moist layer in the vessel and to allow more progressive drying. This solution adopted for vessels of average capacity (60 t ladles), is not satisfactory for vessels of greater size.
It will be also noted that good toughness of the refractory materials does not depend only on the quality of the drying operation to which the refractory is subjected. More particularly, the bottoms have an increasingly defective toughness in proportion as their diameter increases (weight increase), independently of the care taken in drying them. It then appears that sintering alone is insufficient to guarantee good toughness for a considerable mass of refractory. Vessels used in metallurgy have increasingly great dimensions and this tendency is growing, which makes the problem of the toughness of the refractory lining more acute.